Figure 2. Polymer and nanocarbon materials molded in the VFD. (a)
Crystallization and self-assembly of C60 under shear
stress in toluene at a concentration below saturation level, resulting
in (i) spicules, (ii) rods, and (iii) mixes of spicules and rods formed
at 4000, 7000 and 6000 rpm, corresponding to specular flow, transitions
from specular to double-helical flow and helical flow, respectively. (b)
Creating (i) regular and (ii) irregular cones of self-assembled
C60 in a 20 mm OD tube, with (iii) and (iv) being
sharper pitch cones with extended arms in a 10 mm OD tube, formed by
micro-mixing a 1:1 solution of C60 in o -xylene
and DMF, θ 45°, 20 mm OD tube, with (v) Cones fastened to the wall of
the glass tube, 10 mm OD tube. (c) (i and ii) Patterns of the holes
arising from double-helical flow, formed at the interface of the glass
tube and a thin polysulfone film (~ 5 µm) formed in
toluene at 20°C, θ 45°, 7000 rpm rotational speed, along the length of
the tube, with the arrow designating the direction of the rotational
axis of the tube29. (d) Cartoon of the relative film
thickness on the upper and lower side of the rotating hemispherical
based quartz tube (20 mm OD, 17.5 mm ID) when processing a mixture of
water and toluene; two types of fluid flows presented in the thin film
were spinning top and double helical topological fluid flows. (e) Film
thickness derived from neutron imaging. (f) Layer thickness as a
function of height up the tube and rotational speed. (a-c) Reproduced
under the terms of CC BY 3.0 license29. Copyright
2021, Royal Society of Chemistry. (d-f) Reproduced under the terms of
Creative Commons Attribution 3.0 Unported License14.
Copyright 2022, Royal Society of Chemistry.
We recently established that the VFD can centrifugally separate
immiscible liquids of different densities in a θ 45° inclined rotating
tube without using phase transfer catalysts, microgels, surfactants,
complex polymers, nanoparticles, or micromixers14.
Depending on the properties of the two liquids, the micro to submicron
size topological flow regimes in the thin films discussed previously
caused substantial inter-phase mass transfer. A Coriolis force is
produced from the hemispherical base of the tube which is the spinning
top topological fluid flow. This is present in the less dense liquid but
penetrates the denser layer of liquid, transporting liquid from the
upper layer through the lower layer to the surface of the tube. In a
similar way, double helical topological flow in the less dense fluid
caused by Faraday wave eddy currents being twisted by Coriolis forces,
also impact of the surface of the tube. Through the self-assembly of
nanoparticles at the interface of the two liquids, the lateral
dimensions of these topological flows have been identified, Figure 3a.
When a threshold rotational speed is achieved, double helical flow also
occurs in the denser layer at high rotational speeds, which results in
preformed emulsions of two immiscible liquids rapidly phase separating.
By altering the shape of the base of the tube while maintaining rapid
mass transfer between phases, it is possible to perturb the spinning top
flow relative to double helical flow while avoiding the necessity for
phase transfer catalysts, Figure 2d and 3b. The results discussed here
have implications for overcoming mass transfer limitations at liquid
interfaces and presenting innovative technologies for extraction and
separation research, all while preventing the creation of emulsions.